The present invention relates generally to a system and method used in conjunction with an implantable medical device. More particularly, the present invention relates to a system and method for controlling an implantable medical device based upon sensed information indicative of hemodynamic stability.
Cardiac disease affects millions of people throughout the world. Cardiac disease may cause the excitatory and conductive systems of the heart to fail, resulting in an abnormal cardiac rhythm, usually referred to as arrhythmia. Some arrhythmias are very dangerous, and may lead to death of the patient. Other arrhythmias may be the origin of less threatening conditions, but for which medical treatment is nevertheless required. One of the possible treatments for patients suffering from arrhythmia is assistance by an implantable medical device (IMD).
Modern IMDs, such as pacemakers or defibrillators, are complicated electronic devices generally configured to deliver an electrical stimulation to the patient""s heart. Alternatively, the IMD can be a drug delivery device, providing controlled distribution of an appropriate drug therapy. Regardless, IMDs are capable of providing assistance on demand, i.e., when the excitatory and conductive systems of the heart fail to operate normally. In order to accommodate specific patient needs, an IMD is normally part of an overall system that constantly monitors heart activity such that the resulting delivered therapy is optimal for the patient.
Overall IMD systems known in the art comprise several components, including the IMD, pacing and/or sensing leads, and a processor. For most applications, the IMD system is pre-programmed to effectuate a desired therapy routine. Often times, it is extremely useful to utilize feedback information from the patient""s heart to alter and optimize the therapy routine. To this end, the sensing leads are available for sensing certain cardiac parameters and providing information relating to functioning of the heart, usually on a beat-by-beat basis. The processor analyzes these sensed activities and, based upon appropriate algorithms, determines an optimal therapy, both short-term and long-term. For most pacing applications, two sensing leads are typically provided, one deployed in a heart atrium and the other in a heart ventricle. With this arrangement, an electrocardiogram (ECG) signal is sensed and analyzed. As is well known, the ECG signal provides information indicative of atrial depolarization (P-wave), ventricular depolarization (QRS-wave), and ventricular repolarization (T-wave). Numerous efforts have been made to distinguish the various waves from one another, as well as to classify whether individual wave components indicate heart abnormalities.
For example, previous efforts have been made to utilize ventricular repolarization (ventricular T-wave) information to control a rate response, AV delay, and to predict arrhythmias. Examples of such applications are provided in Table 1 below:
All patents listed in Table 1 are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments, and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.
Noticeably absent from prior cardiac sensing and analyzing systems is information relating to atrial repolarization (atrial T-wave or atrial PT-wave). Due to the relatively small electrical activity associated with atrial repolarization and because atrial repolarization occurs during the predominant ventricular depolarization, it has previously been assumed that atrial repolarization is impossible to sense, as evidenced by the patents listed in Table 2.
All patents listed in Table 2 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments, and claims set forth below, many of the devices and methods disclosed in the patents of Table 2 may be modified advantageously by using the teachings of the present invention.
More recently, the ability to sense atrial repolarization has become possible. In particular, the advent of digital signal processing (DSP) has provided a tool that can be employed to effectively sense atrial repolarization. In this regard, Wolgemuth, U.S. Pat. No. 6,029,087, issued Feb. 22, 2000, the teachings of which are incorporated herein by reference, describes in detail DSP solution for sensing, processing, and classifying intracardiac signals so as to provide the IMD with reliable cardiac event data via DSP technology. Through the event classification based upon DSP information described by Wolgemuth, atrial repolarization, and thus total atrial cycle time for a heartbeat can now be sensed.
One disadvantage of prior art systems, including those listed in Tables 1 and 2 above, relates to the inability to utilize atrial repolarization information in controlling and/or optimally setting a specific IMD implanted in a specific patient. Therefore, there is a continuing need for a system and method that evaluates cardiac functioning utilizing atrial repolarization information for optimizing IMD therapy.
The present invention overcomes the disadvantages of the prior art by providing a method of, and a system for, controlling an IMD based upon atrial cycle time, including atrial repolarization, information.
The present invention has certain objects. That is, the present invention provides solutions to certain problems existing in the prior art such as: (a) an inability to utilize the atrial repolarization portion of a cardiac signal to evaluate functioning of a heart; (b) an inability to utilize the atrial repolarization portion of a cardiac signal to control an implantable medical device; (c) an inability to predict short-term deviations from a hemodynamic situation; (d) an inability to control an implantable medical device to correct short-term deviations from a hemodynamic situation; (e) an inability to predict long-term deviations from a hemodynamic situation; (f) an inability to control an implantable medical device to correct long-term deviations from a hemodynamic situation; (g) an inability to evaluate heart operation based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time; (h) an inability to control an implantable medical device based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time.
The system and method of the present invention provides certain advantages including: (a) the ability to utilize the atrial repolarization portion of a cardiac signal to evaluate functioning of a heart; (b) the ability to utilize the atrial repolarization portion of a cardiac signal to control an implantable medical device; (c) the ability to predict short-term deviations from a hemodynamic situation; (d) the ability to control an implantable medical device to correct short-term deviations from a hemodynamic situation; (e) the ability to predict long-term deviations from a hemodynamic situation; (f) the ability to control an implantable medical device to correct long-term deviations from a hemodynamic situation; (g) the ability to evaluate heart operation based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time; (h) the ability to control an implantable medical device based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time.
The system and method of the present invention has certain features, including sensing atrial cycle time and ventricular cycle time for a particular heartbeat. The atrial cycle time includes the atrial repolarization period. A hemodynamic baseline ratio is generated based upon the atrial cycle time and the ventricular cycle time of an electrical heartbeat representing the hemodynamical cycle time of a heartbeat. Also, an active ratio is generated based upon an atrial cycle time and a ventricular cycle time of an active heartbeat. By comparing the hemodynamic baseline ratio and the active ratio, a corrective action can be determined. In this regard, a medical device is controlled to effectuate the determined corrective action. Essentially, then, electrical signals provided by the heart are sensed and then linked or correlated to a hemodynamical situation that results from the electromechanical coupling in each chamber of the heart.